In collaboration with investigators at Brigham and Women's Hospital, this study will evaluate the association between altered hormonal and renal blood flow response to angiotension II, sodium sensitivity, decreased urinary kalikrein excretion, low plasma renin activity, altered erythrocyte ion transport, and increased 6-beta hydroxycortisol production with essential hypertension in African-Americans. The possible genetic linkage of the above phenotypes with essential hypertension will also be evaluated.